B05: Analysis of the effect of a pressure gaining combustion on the film cooling efficiency of turbine blades

Summary

This project is part of the Collaborative Research Cluster 1029 TurbIn – Substantial efficiency inrease in gas turbines through direct use of coupled unsteady combustion and flow dynamics.

In the course of this particular project the influence of a pulsating and highly unsteady turbine flow, which is a result of the novel combustion process, on the film cooling efficiency of a turbine blade shall be examined. The main goal is to ensure the functionality of the film cooling for all resulting boundary conditions and, if possible, to identify means to reduce the necessary secondary cooling massflow which would result in an overall efficiency gain.

The injection of cooling flow generates a uniform film cooling flow along the blade surface which not only blocks off the hot main gas from the surface but also acts as a heat sink as it lowers the mean temperature within the boundary layer. If properly designed and adjusted, the film cooling flow will cover the whole blade surface whereas for an imperfect flow the thermal stress will rapidly damage and/or destroy the blade. It is therefore necessary to examine the influence of both the pressure and velocity fluctuations on the cooling flow field.

An unsteady Low-Speed test facility is used in the beginning to examine the basic influence of the pressure fluctuations on the film cooling. The large scaling of the measurement section and its optical access allows a very good time-resolved and spatial resolution of this influence.

The succeeding experiments will be carried out at the Hot-Acoustic-Testrig (HAT) which will focus on the influence of the pressure fluctuations on film cooling flow for high temperatures.

Person of contact: Dipl.-Ing. Alexander Heinrich

1st Funding period 2012 - 2016

Summary

Within the B05 project we examine the impact of a pulsed combustion on the turbine sealing cavity, which prevents hot gas ingestion into the inner machine. Sealing flow is ensured by secondary air blowing radially through the rotor-stator-wheel space. However, the interaction between the sealing flow and the main gas flow causes aerodynamic losses. These losses as well as the use of secondary compressor air should be kept at a minimum in order to increase the efficiency of the whole machine. The Hot-Acoustic-Testrig (HAT, see Fig. 1) allows an investigation of the subject under realistic flow conditions, such as high temperature and pressure.

For this, a specific measurement section has been designed, which features a plenum to provide secondary air to the main flow. To simulate a pressure increasing combustion, a setup with multiple fast shifting valves was realized. The unsteady flow is measured by pressure tabs with a high time resolution. In a next step a characteristic linear cascade was designed to replace the turbine stator and generate a typical stator wake. Measurements of the total pressure loss over the cascade vanes have been conducted by means of a five-hole probe and by Particle Image Velocimetry. A considerable pressure loss inside the vane wake was observed at a Mach number Ma = 0.35. Figure 2 shows a PIV image of the averaged velocities downstream in the wake of the stator.

Schliwka, T., Tiedemann, C. and Peitsch, D.: Interaction of Main Flow and Sealing Air across a Turbine Cavity under unsteady conditions; T., International Symposium on Air Breathing Engines, Phoenix, USA, ISABE-2015-21288, 2015